<style>

</style>
<body>
    <input type="button"value='开启计时器' id="btn1">
    <input type="button"value='开启计时器' id="btn2">
    
</body>
<script>
     var obtn1 =document.getElementById('btn1')
     console.log(btn1)
     var obtn2 = document.getElementById('btn2')
     obtn1.onclick = function(){
        console.log(123)
     }
    
</script